1. Field of the Invention
The present invention generally relates to a method for maintaining a smooth surface of material, and more particularly to a method for maintaining a smooth surface of crystallizable material.
2. Description of Related Art
Generally speaking, in the forming process of crystallizable materials, it is common to form a seed layer which is used as a crystal growth center. Then, a target crystallizable material is further formed based on the seed layer. The materials of the seed layer and the target crystallizable material can be the same or different. FIGS. 1A-1B show crystal-growth steps corresponding to formation of conventional zinc oxide nanorods. First, referring to FIG. 1A, a substrate 110 is provided, and a zinc oxide seed layer 120 is formed on the substrate 110. Then, referring to FIG. 1B, zinc oxide nanorods 150 are formed, wherein the zinc oxide seed layer 120 is used as a crystal growth center.
The dimension of the zinc oxide nanorods 150 is related to the crystallization of the zinc oxide seed layer 120. When the grain size of the zinc oxide seed layer 120 is larger, coarse zinc oxide nanorods 150 can be formed; when the grain size of the zinc oxide seed layer 120 is smaller, smaller zinc oxide nanorods 150 can be formed. In order to adjust the grain size of the zinc oxide seed layer 120, an annealing treatment can be implemented to the zinc oxide seed layer 120 for adjusting the crystallization of the zinc oxide seed layer 120. When the temperature of the annealing treatment is higher, the grain size of the zinc oxide seed layer 120 is bigger; when the temperature of the annealing treatment is lower, the grain size of the zinc oxide seed layer 120 is smaller. By controlling the temperature of the annealing treatment, the dimension of the zinc oxide nanorods 150 can be controlled thereby.
However, when the temperature of the annealing treatment is higher, the grain size of the zinc oxide seed layer 120 is larger, leading to a rough and uneven surface of the zinc oxide seed layer 120. The subsequently formed zinc oxide nanorods 150 will not grow in (e.g., towards) substantially the same direction and will not form an ordered array.
For the disadvantages of the prior art mentioned above, there remains a need to provide a method for maintaining a smooth surface of material. The surface of the material should be maintained smooth after the annealing treatment. High quality nano-structures could then be formed by using the smooth surface of material as a crystal growth center.